Say you have the user enter in a number 0-3 and want to test it. The most common way seems to be:
[[ $var =~ ^[0-3]$ ]]
But how would you use this with:
test expression
My initial attempt doesn't evaluate correctly, e.g.
read -p "Enter selection [0-3] > "
if test $REPLY == '^[0-3]$' ; then
...
It just evaluates the if statement as false.
test is equivalent to the [ ] structure, but not to [[ ]], which is an extended version. The regex =~ is only available in the extended test, so for simple test or [ ] you have to pull the regex evaluation from elsewhere.
One fix is grep. This pipeline will catch and print the matches:
echo "$REPLY" | grep '^[0-3]$'
Using test with a string evaluates positively if the string is non-empty. Compare these two:
test "" && echo ok
and
test "a" && echo ok
Knowing this, it's now easy to build a compound test from the both elements.
test "$(echo "$REPLY" | grep '^[0-3]$')"
And this can be applied to the script:
read -p "Enter selection [0-3] > "
if test "$(echo "$REPLY" | grep '^[0-3]$')"; then
...
fi
You can use a regex in Bash like this:
echo -n "Your answer> "
read REPLY
if [[ $REPLY =~ ^[0-9]+$ ]]; then
echo Numeric
else
echo Non-numeric
fi
Please check the post Using Bash's regular expressions.
testcommand does not support regular expressions. useexprinstead: stackoverflow.com/questions/7159441/…test "$var" = 0 || test "$var" = 1 || test "$var" = 2 || test "$var" = 3 && echo okay